The present invention relates to a method of recording and reproducing video data signals, and more particularly to a method of recording and reproducing video data signals in order to improve the quality of a reproduced picture during operation of a digital video cassette recorder (VCR) at a variable speed, such as during a fast-forward, still-frame, or slow-motion operation.
Examples of recording and reproducing techniques for digital VCR are found in the following articles, which are incorporated herein, by reference:
"A Study on Trick Plays for Digital VCR," by Yamamitsu et al., THPM 13.2, pp 184-185, IEEE 1991.
"An Experimental Study for a Home-Use Digital VTR," by Yamamitsu et al., IEEE Transactions on Consumer Electronics, Vol. 35, No. 3, Aug. 1989.
"Rate-Constrained Optimal Block-Adaptive Coding for Digital Tape Recording of HDTV," by Wu and Gersho, IEEE Transactions on Circuits & Systems for Video Technology, Vol. 1, No. 1, March 1991 (pp 100-101).
"Adaptive DCT Coding for Home Digital VTR," by Dol et al., GLOBECOM 1988, pp. 1073-1079.
Because the amount of data in a digitized video signal is massive, the conventional digital video cassette recording/reproducing apparatus (VCR) transforms the image data using a discrete cosine transformation (DCT), which is a type of orthogonal transformation. In order to compress an amount of data, the digital VCR quantizes a DCT coefficient, encodes the quantized coefficient representing the DCT coefficient value by a variable length coding scheme such as a Huffman code, and records the encoded video data on a magnetic tape. Also, the digital VCR reproduces the original image signal by reversing the recording process. Video data representing a single field is recorded onto plural tracks of the magnetic tape through rotary heads when recording the data. To record video signals with high definition by a rotary head-type VCR mechanism designed to record a National Television System Committee (NTSC) standard television signal, the relative velocity of the rotary head to the tape is high. Therefore, a segment recording method is used which distributes and records video signals representing a single field onto a plurality of tracks. Accordingly, it is desirable that on each track there is recorded a constant amount of data corresponding to a fixed portion of the size of the picture. However, since a variable length coding scheme is adopted as described above, it is difficult to fix a constant amount of data assigned to each track to be proportional to a fixed portion of the size of the picture. As a result, when a reproducing head crosses tracks, as when a rapid tape speed is required, it is difficult to obtain the desired picture from data read during the crossing track reproduction operation.
As shown in FIG. 1, a conventional recording format uses a segment recording method having four tracks per field, wherein a head traversely crosses four tracks during a single scan in reproducing at a four-fold speed. Thus, a single track includes data 1a, 1b, 1c, and 1d, constituting one fourth of a field and occurs on the tape as recorded and/or reproduced at normal speeds. At a fast speed of 4 times normal, the reproducing head will cross into four tracks on a single scan, reading data 1a, 1f, 1k and 1p. The video data corresponding to one field is reproduced as shown in FIG. 2, wherein sixteen tracks are scanned four times. Therefore, the image data of a field reproduced at a four-fold speed whose segments in each field are mixed, differs from the image data of a field when reproducing at a normal speed. Moreover, when the coding lengths per track are different for each field, the picture quality reproduced at a variable speed is further deteriorated.